Switch for electric discharge devices



P 1, 1943- M. A. TOWNSEND 2,330,161

SWITCH FOR ELECTRIC DISCHARGE DEVICES Filed Sept. 19, 1941 lnvawkor ark A. Townsend, b MM His At'tovneg.

Patented Sept. 21, 1943 swrron FOR ELECTRIC DISCHARGE nEvICEs Mark A. Townsend, Cleveland Heights, Ohio, assignor to General Electric Company, a corporation of New York Application September 19, 1941, Serial No. 411,547

12 Claims. (01. 200-122) This invention relates to the starting of electric discharge devices, and is here illustrated and explained: as applied to, the starting of a fluorescent lamp. In suitable forms of construction, the invention affords a simple, rugged, durable and reliable switch device that performs the necessary operations for starting a lamp quite automatically, and with proper timing-to assure success, and can be made to repeat the starting action very promptly, when necessary: e. g., if the lamp does not start, directly after its main switch is closed, my switch can keep the lamp cathode(s) properly heated, and meanwhile 'rapidly open and close the starting: circuit again and again until proper starting is achieved, if it is possible. I

A type of switch that would seem very suitable and convenient for starting discharge devices is one in which the circuit is made and broken by thermostaticaction controlled by the heat of a discharge involving the switch devicev itselfcommonly knownas a glow-switch. While glowswitches have been used for startingfluorescent lamps, diiilculty has been experienced in making a simple-inexpensive, and reliableglow-switch device which will remain closed long enough to assure proper heating of the lamp cathodes before it opens. yet will open with sufficient promptitude to minimize the period of darkness between the closing of the main lamp switch and the actual starting or lighting up of the lamp. This, however, can readily be accomplished-by a switch constructed in accordance with my invention, without dependence on such factors as the nature and pressure of the atmosphere in a discharge device .to control the timing of the switch action.

In carrying out my invention as hereinafter described, thermostats oi diilerent characteristics are correlated to coact in controlling the starting circuit, one of these thermostats being relatively fast-acting, and the other relatively slowacting. By suitable correlations of such thermostats, the circuit can be made and broken in such a way as to secure modes of operation very favorable for starting a discharge device or lamp: e. g., they may be so correlated as to assure that the switch will remain closed long enough to preheat the cathodes of the discharge device sufflciently for starting the lamp successfully, yet no longer than is really needful. Such thermostats can also be correlated to give other modes of operation of the switch, for other purposes. The diflerent characteristics -or degrees of sensitiveness or of quickness of response of the thermostats may be produced in various ways, including wiring connections for an electric discharge device including my starting switch; Fig. 2 is a side view of the essential parts of one form of my switch on a larger scale; and Fig. 3 is a tilted or perspective view of the essential parts of another form of my switch.

Fig. 1 shows an ordinary fluorescent lamp L of positive column electric discharge type with a tubular envelope in having the usual spacedapart activated thermionic cathodes II, II in its ends, which may be specially heated cathodes of usual coiled filament type, and are shown con-' nected across a power-supply circuit P including the usual ballast H, which also serves as a starting inductance, and the manual make-and-break switch IS. The envelope it may contain a lowpressure atmosphere of starting gas, such as argon, and also a vaporizable and ionizable working substance such as mercury. A surplus supply of mercury, exceeding the amount that will vaporize during operation of the lamp L, is indicated by a drop ll inside the envelope l0, and an internal coating of fluorescent material or phosphor II on the envelope walls is also indicated. A starting and electrode-heating circuit H is shown connected across the circuit P through the filamentary cathodes II, II, with my starting switch S included therein.

The general mode of operation in starting a lamp L with this circuit arrangement is that when the switch I5 is closed to turn on the lamp L the switch device '8 permits flow of current through the circuit H and the cathode filaments II, II in series therein for a suflicient length of time to preheat the cathodes to an adequate emissive temperature, and then suddenly opens the circuit H, and that the resulting voltage kick across the cathodes H, H suiflces to initiate discharge between them-or, in other words, starts the lamp.

As shown in Figs. 1 and'2, my switch S is of glow-switch type, comprising a glass envelope ple.

containing a low pressure atmosphere of rare gas, such as argon at an absolute pressure of mm. of mercury. The envelope 20 may include a stem 2i through which are sealed current leads 22, 23 that are connected to'opposite sides of the circuit H, and are provided with terminals or electrodes inside the envelope between which a glow discharge takes place when the switch I5 is first closed. The lead 22 may have an extension (of nickeLfor example) inward or upward from the stem 2| to serve as one terminaL'while the other termlnalmay be formed by the end of a thermostatic'bimetal strip member 25 that is I According to the direction of flexure of the bimetal strip 25 with rising temperature, its contact 28 may lie at either side of the lead 22: as here shown, it lies outside, to the right or the lead, and bends in against the lead when heated.

For also and additionally connecting the member 25 to the lead 23, there is another thermostatic bimetal strip member 30, here shown as welded at one end 3| to the fixed end of the member 25, and bent over so that its other free end lies adjacent the lead 23, and provided with a welded-on contact 32, of molybdenum, for exam- The member being arranged to bend outward to the right when heated, its contact 32 lies inside and to the left of the lead 23, whose portion extending up beyond the stem 2| may be of nickel, for example. Besides the heat of the glow discharge between the contact electrodes 22 and 28, there is an electric resistance .coil heater 36 for heating the thermostats 25 and 30, interposed in the connection 26 from the lead 23 to a mid-portion of the member 25-between the point of attachment of the member 30 and the electrode contact 28. The thermostat 25 is made more sensitive or more quickly responsive to heat than the thermostat 30, which may be accomplished as suggested in the drawings by making the member 25 a longer and narrower strip than the member 30, though of exactly the same bimetallic sheet material. Both the strips 25 and 30 may be of the laminated sheet material that is marketed as Chace #2400 Bimetal," which is more particularly describedhereina fter.

When line voltage is applied "tothecircuit H and across the leads 22, 23"as a result of closing the switch 15, a glow discharge occurs across the small gap between lead 22 and electrode 28 and otherlparts that are connected to lead 23, heating the parts nearby, including both thermostats 25 and 30. Being very sensitive or responsive, the thermostat 25 quickly closes the contacts 23, 28, short-circuiting and terminating the glow discharge. The resulting larger short-circuit current of the circuits P and H then flows through heater and thermostatic member 25, heating the heater 36 more rapidly. The heater 55 is so located between the parts 25 and 30 that thermostat 25 remains closed, after extinction of the glow discharge, while the less sensitive or responsive thermostat 30 gradually heats up. After an interval which depends on factors due to the design and relative locations of the partsincluding the position and resistance of heater 36, and the short-circuit current flowing-the thermostat 30 closes the contacts 23, 32, thus shorting out the heater 36 so that it is no longer effective. This allows the thermostat 25 to cool and open the-contacts 28, 22, thus breaking the heating circuit H and producing a voltage kick that starts the lamp L. Thereafter, the voltage available across the gap between the glow-switch parts 22, 28 is insufficient to produce a discharge, so that the entire current flow of the circuit P is through the discharge in the lamp L,

It will be seen that by adjusting the position of the heater 36 relative to the thermostats 25 and 30, between which it is located, the action of the device and the time during which the circuit H is closed can be adjusted as desired, quite independently of the filling gas in the envelope 20, and that the design of the thermostat 25 is less restricted for the same reason.

Fig. 3 illustrates another form of glow switch construction, in which U-bent thermostatic strips 25a and 30a are arranged alongside one another in parallel planes, instead of one within the other in the same plane, as in Fig. 2, and have their fixed ends welded to the main portion of a common support wire 21a, which is bent to extend crosswise of the leads 22a, 23a, while its lower end is fused into the glass stem 2 la. The molyb denum contacts 28a, 32a on the free ends of the thermostat members 25a, 30a coact with upstanding nickel extensions of the lead wires 22a, 23a, which are connected to opposite sides of the starting circuit H. The coil heater 36a is connected between the upper end of the lead 23a and the upstanding end of the support wire 21a, and extends crosswise of the members 25a, 30a through their U-bends. As here shown, the gap between the contact 28a of thefquicker acting thermostat member 25a and the lead 22a is considerably less than that between the contact 3241 of the slower acting thermostat member 30a and the lead 23a. The coil heater 36a is shown with a single turn or convolution 31 associated with the bend of the quicker acting thermostat 25a, underneath the same, as against some half a dozen turns or convolutions 38 more especially associated with the slower acting thermostat 30a, underneath the same and to the left thereof, toward the thermostat 25a.

In operation, the glow discharge takes place across the gaps-between the lead 22a and the thermostats-"25a, 30a, both of which are connected to the lead 23a, heating the thermostats ./about equally until the thermostat 25a closes the shorter gap and thus shorts out the discharge. The heat due to the increased current flow through the coil 31 of the heater 36a keeps the thermostat 25a. hot enough to remain closed, and the coils 38 gradually heat up the thermostat 30a, which eventually closes the longer gap between the parts 23a and 3011, thus shorting out the heater. The thermostat 25a quickly cools and opens the circuit H, thus starting the lamp.

For the convenience Qf thOSB wishing to use my invention, the following illustrative particulars of a device of the Fig. 3 type are given:

The thermostatic members 25a, 30a may be strips of the bimetal marketed as Chace #2400 Bimetal, composed of; laminae of Invar, an alloy of 64 per cent iron and 36 per cent nickel, and of chrome iron, an alloy of 75 per cent iron, 22 per cent nickel, and 3 per cent chromium, in 75 equal thicknesses, welded together. Each of the strips may be 0.006 inch thick, 16 mm. long, and 2 mm'Iwidaand bent to a U about 7 mm. long, with a semi-circular bend of 3 mm. diameter. The two U-members 25a, llla may be spaced apart about 4 mm. horizontally. The support wire 21a may extend upward about 2 mm. from the stem 2! a t its first bend, then mm. horizontally to'the left, and then upward 6 mm. to the point where the heater wire is welded to it. The lead 22a may extend upward 4 mm. above the horizontal portion of the support 21a, and the lead 23a may extend upward to a level with the upper end of the support 21a, sloping outward so that its upper end is 10 mm. to the right or the upper end or the support. When the device is at ordinary atmospheric temperature, the gap between contact 28a and lead 22a may be V2 mm., and that between contact 320 and lead He may be 1 mm. The heater "a may be a coiled coil or 1.9 mil tungsten wire, being first coiled 335 turns per inch on a 4 mil mandrel, and then coiled on a 16 mil mandrel. The single heater turn 81 and the lead 22a may both be centered in the middle of the "thermostat strip a, and the group of turns 38 may start two mils to the right of the turn 31 and extend about 2 /2 mils further to the right, comprising 6 turns wound at a pitch of about 70 turns per inch. Like the glow switch illustrated in Fig. 2, that of Fig. 3 may contain an atmosphere of argon at a pressure of 25 mm.

What I claim as new and desire to secure by Letters Patent 0! the United States is:

1. A starting switch for a starting circuit of an electric discharge device comprising correlated thermostats, one relatively fast-acting and another relatively slow-acting, responsive to heat developed before and after the switch closes in its operation to start the discharge in said discharge device, and coacting to control said starting circuit.

2. A starting switch for a starting circuit of an electric discharge device comprising correlated thermostats, one relatively fast-acting and another relatively slow-acting, responsive to heat of a discharge and of the starting current through the aforesaid discharge device when the discharge in said device is being started, and coacting to control said starting circuit.

3. A starting switch for a starting circuit of r an electric discharge device comprising, in combination, a switch device for closing said circuit including glow discharge means and thermo-responsive means exposed to be heated by the glow discharge, and eifective to terminate the glow discharge when closing said circuit; and slower acting thermo-responsive means also controlling said circiut, and responsive to heat developed by current flow when the circuit is closed.

4. A glow switch for a starting circuit of an electric discharge device comprising, in comb nation, a switch device for closing said circuit including glow discharge means and thermo-responsive means exposed to be heated by the glow discharge, and effective to terminate the glow discharge when closing said circuit; and means responsive to current flowing through said switch device when closed for delaying the cooling and opening thereof.

5. A glow switch for a starting circuit or an electric discharge device comprising, in combination, a switch device for closing said circuit including glow discharge means and thermo-responsive means exposed to be heated by the glow discharge, and eflective to terminate the glow discharge when closing said circuit; an electric heater for heating said thermo-responsive means when said circuit is closed; and means for rendering said heater ineffective at an interval of time after the closure 01 said circuit.

6. A glow switch for a starting circuit of an electric discharge device comprising, in combination, a switch device for closing said circuit including glow discharge means and thermo-responsive means exposed to be heated by the glow discharge, and eifective to terminate the glow discharge when closing said circuit; an electric heater for heating said thermo-responsive means when said circuit is closed; and thermo-responsive means exposed to the heat of said heater for short-circuiting the same.

7. A glow switch for a starting circuit of an electric discharge device comprising, in combination, a thermostatic switch for closing said circuit, including coacting electrode and thermostat members, with a circuit connection to one or said members including an electric heater for the thermostat, and means of short-circuit connection past said heater to the member aforesaid including a thermostat member also heated by the heater.

8. A glow switch for a starting circuit of an electric discharge device comprising, in combination, adjacent current leads and a laterally flexible thermostat member electrically connected to one of said leads and coacting with the other in a glow discharge and as a switch contact, an electric heater for said thermostat connected between said leads when said thermostat is closed, and a less sensitive laterally flexible thermostat member for shortcircuiting said heater arranged adjacent the same to be heated thereby.

9. A glow switch for a starting circuit or an electric discharge device comprising, in combination, laterally flexible thermostat members connected to one side of said circuit, an electric heater adjacent said thermostat members for heating them both, a connection from the other side of said circuit for coacting with one of said thermostat members in a glow discharge and as a switch contact for closing said circuit, and means for coacting with the other thermostat member to short-circuit said heater after the closing or the circuit by the first-mentioned member.

10. A glow switch for a starting circuit or an electric discharge device comprising, in combination, a stem with current leads sealed therethrough; a laterally flexible thermostatic member having one end attached to said stem adJacent one of said leads and bent over so that its other and lies adjacent the other 01 said leads, to coact therewith in a glow discharge and as a switch contact; another thermostatic member having one end connected to said first-mentioned member and its other end adjacent the current lead first above mentioned, to coact therewith as a switch contact; and an electric heater extending between said thermostatic members, for heating them both, and electrically connected between said first-mentioned current lead and an intermediate point of the first-mentioned thermostatic member.

11. A glow switch for a starting circuit of an electric discharge device comprising, in combination, a stem with current leads sealed therethrough; a support mounted on said stem and extending crosswise of said leads; laterally flexible thermostatic members each having one end attached to said support and having its other end adjacent said support to coact therewith as a switch contact; and a heater for said thermostatic members extending crosswise of the latter and connected between said support and one of said leads.

12. A glow switch for a starting circuit of an 5 electric discharge device comprising, in combination, a stem with current leads sealed therethrcngh; a support mounted on said stem and extending crosswise of said leads; U-bent flexible thermostatic members each having one end attached to said support and having its other end adjacent one of said leads to coact therewith as a switch contact; and a, heater for said thermostatic members extending crosswise of them through their bends and connected between said support and one of said leads.

MARK A. TOWNSEND. 

